Electromagnetic (EM) telemetry is an example of a communication tool for transmitting drilling mechanics and formation evaluation information uphole, in real-time, from a measurement-while-drilling (MWD) and/or logging-while-drilling (LWD) tool. When compared to conventional mud pulse telemetry, EM telemetry provides higher data transmission rates, better tolerances of lost circulation material (LCM), and rig-independent EM-downlinking. Consequently, it achieves reduced rig-time and lower costs of service delivery.
An uplink EM signal can be collected by at least two stakes on the surface. A blow-out preventer (BOP) can be used as one of the two stakes. Oftentimes, the EM signal may be attenuated (e.g., due to a conductive formation, water-based mud (WBM), and/or noises present at the rig site). Due to this attenuation, it may be difficult to detect a small/weak EM signal. This can make it difficult to decode the information sent out from the gap source in the transmitter, which can include the wide use of EM telemetry.
One solution is to use a steel-cased deep-electrode (DE) well adjacent to the drilling well to measure the signal. Through field tests, it has been confirmed that using deep electrodes as receivers has made it possible to decode EM telemetry signals until its touchdown (TD), e.g., 28,000 ft. However, a challenge with EM telemetry still exists with regard to predicting a real job EM signal knowing some information about the drilling well, DE well, as well as resistivity distribution of the formation. This can be a pre-job 3D EM modeling problem.